Curable composition for coating, and articles coated with it

ABSTRACT

The curable composition for coating of the invention comprises (A) 100 parts by weight of a resin having at least 2 epoxy groups in one molecule and having an epoxy equivalent of from 200 to 2,000 g/mol, and (B) from 0.001 to 100 parts by weight of a compound having at least 2 carboxyl groups in one molecule, in a molar ratio of the epoxy group to the carboxyl group (epoxy group/carboxyl group) of from 0.2/1 to 5.0/1, and contains (C) at least one organic solvent selected from glycol monoalkyl ethers, vinyl ethers and cyclic ethers, and at least one selected from monoalkyl alcohol compounds and compounds capable of giving alcohols through hydrolysis, each in an amount of from 1.0 to 50 parts by weight relative to 100 parts by weight of the total solid resin content of the composition. The composition has good storage stability and good thermal curability, and the coating films from it have good acid resistance, scratch resistance and weather resistance.

TECHNICAL FIELD

The present invention relates to a curable composition for top coating,and to articles coated with it. Precisely, it relates to a curablecomposition for top coating favorable for cars, industrial machines,steel furniture, interior and exterior decorations for constructions,household electric appliances, plastic goods, etc., and to articlescoated with the composition. More precisely, the invention relates to acurable composition for top coating, which forms coating films havinghigh acid resistance and scratch resistance, good outward appearance,high waterproofness and weather resistance, and high hardness, and whichhas good storage stability, and to articles coated with it. Thecomposition is especially favorable for top coating cars.

BACKGROUND ART

For coating cars, industrial machines, steel furniture, interior andexterior decorations for constructions, household electric appliances,plastics and others, coating compositions consisting essentially ofmelamine resins such as alkydmelamines, acrylic melamines and the likehave heretofore been used.

However, the conventional coating compositions consisting essentially ofsuch melamine resins are problematic in that they generate a largeamount of harmful formalin when cured, and that the cured films havepoor acid resistance and are therefore often corroded by acid rain. Inparticular, the problem with acid rain caused by recent air pollutionhas become more serious, and the conventional coating films are oftenetched, whitened or stained by acid rain.

In order to solve this problem, a coating composition has been proposedin Japanese Patent Application Laid-Open (JP-A) Hei-2-45577 andHei-3-28650, in which are formed ester bonds that act as crosslinkingpoints, through reaction of an acid with an epoxy group.

The coating film of the proposed composition has good acid resistance,but is still defective in that it is whitened in an accelerated weatherresistance test. In addition, the low-temperature curability of thecomposition is poor, the coating film of the composition formed aroundcar bodies is often scratched with brushes when the car bodies arewashed with a car washer, and the storage stability of the compositionis poor.

For finishing car bodies by top coating, generally employed is any oftwo types of metallic color finishing and solid color finishing.

For the metallic color finishing of those two, generally employed is a2-coat 1-bake method of heating and curing coating composition, whichcomprises coating a substrate with a metallic base coat followed byovercoating it with a clear coat of an acrylic melamine resincomposition in an wet-on-wet system.

For the other solid color finishing, generally employed is a 1-coat1-bake method of using an alkydmelamine resin composition, in which thecomposition is heated and cured to form top coating. For recent severerequirements for the properties of coating films, including, forexample, finish appearance, weather resistance, acid resistance, scratchresistance and stain resistance thereof, a method of overcoating a solidcolor-finished substrate with a clear coat of an acrylic melamine resincomposition or the like has been proposed. However, even in the proposedmethod of overcoating the solid color finish with such a clear coat,coated articles having the properties of good acid resistance, goodscratch resistance and good weather resistance could not as yet beobtained.

The present invention has been made in consideration of the currentsituation noted above, and its object is to provide a curablecomposition for top coating, which has good thermal curability to formgood coating films having good acid resistance, weather resistance,waterproofness, scratch resistance and outward appearance, and whichadditionally has good storage stability. In particular, the compositionforms excellent clear coats when used in forming car bodies. Theinvention further provides articles as coated with the composition.

DISCLOSURE OF THE INVENTION

The curable composition for top coating of the invention comprises (A)100 parts by weight of a resin having at least 2 epoxy groups in onemolecule and having an epoxy equivalent of from 200 to 2,000 g/mol, and(B) from 0.001 to 100 parts by weight of a compound having at least 2carboxyl groups in one molecule, in a molar ratio of the epoxy group tothe carboxyl group of from 0.2/1 to 5.0/1, and contains (C) at least oneorganic solvent selected from glycol monoalkyl ethers, vinyl ethers andcyclic ethers, and at least one selected from monoalkyl alcoholcompounds and compounds capable of giving alcohols through hydrolysis,each in an amount of from 1.0 to 30 parts by weight relative to 100parts by weight of the total solid resin content of the composition.

In the curable composition for coating noted above, the resin of thecomponent (A) may have alcoholic hydroxyl groups in a ratio of notsmaller than 400 g/mol in terms of the hydroxyl equivalent, and havehydrolyzable silyl groups in a ratio of not smaller than 500 g/mol interms of the hydrolyzable silyl equivalent; and the component (B) may bean oligomer compound as obtained through half-esterification of a polyolcompound with an acid anhydride to have at least 2 carboxyl groups inone molecule and have a molecular weight of not larger than 2,000.

The curable composition for coating of the invention may contain (D) acuring catalyst in an amount of from 0.001 to 10 parts by weightrelative to 100 parts by weight of the total solid content of thecomponents (A) and (B).

The curable composition for coating of the invention may contain (E) ahydroxyl group-having resin in an amount of from 0 to 80 parts by weightrelative to 100 parts by weight of the total solid content of thecomponents (A) and (B).

The hydroxyl group-having resin of the component (E) may be composed offrom 5 to 30 parts by weight of at least one, hydroxyl group-havingvinylic monomer and from 70 to 95 parts by weight of at least onevinylic monomer having no hydroxyl group. The resin may be a non-aqueousdispersed polymer to be prepared through dispersion polymerization of atleast one, hydroxyl group-having vinylic monomer and at least onevinylic monomer having no hydroxyl group in an organic solution thatcontains an organic solvent-soluble polymer having a number-averagemolecular weight of from 1,000 to 25,000, and the non-aqueous dispersedpolymer thus prepared is insoluble in the organic solution.

The curable composition of the invention may further contain (F) anamino resin in an amount of not larger than 30 parts by weight relativeto 100 parts by weight of the total solid content of the components (A)and (B).

The coated article of the invention has a clear top coat as formed overthe surface of the substrate previously coated with a coatingcomposition that contains metallic powder and/or color pigment, in whichthe clear top coat consists essentially of the composition of theinvention noted above.

The terminology “vinylic” as referred to herein is meant to indicate thegroup derived from a compound having polymerizable C═C bonding, such asvinyl group, vinylidene group, etc.

BEST MODES OF CARRYING OUT THE INVENTION

The constituent components (A) to (F) and others that may constitute thecurable composition for top coating of the invention are described belowin order.

Component (A)

The component (A) of the basic, epoxy group-having resin for use in theinvention includes, for example, the following four types of resins [1],[2], [3], [4]:

[1] Epoxy group-having resin (hereinafter referred to as “resin [1]”).

[2] Resin having both epoxy and hydroxyl groups (hereinafter referred toas “resin [2]”).

[3] Resin having both epoxy and hydrolyzable silyl groups (hereinafterreferred to as “resin [3]”).

[4] Resin having all epoxy, hydrolyzable silyl and hydroxyl groups(hereinafter referred to as “resin [4]”).

These resins [1] to [4] are described below.

[Resin [1] (epoxy group-having resin)]

Resin [1] is composed of units from epoxy group-having vinylic monomers,and units from other copolymerizable vinylic monomers, etc.

The copolymerizable, epoxy group-having vinylic monomers are notspecifically defined, and include, for example, those of the followinggeneral formulae (1) to (14):

In those general formulae, R¹ represents a hydrogen atom or a methylgroup, and R² represents a divalent aliphatic saturated hydrocarbongroup having from 1 to 6 carbon atoms.

The amount of the epoxy group-having vinylic monomers to be in resin [1]is preferably from 10 to 70%, more preferably from 20 to 60% of thetotal amount of the comonomers therein. If the amount of those monomersis smaller than 10%, the composition to be obtained herein could nothave good curability and acid resistance. However, if the amount islarger than 70%, the compatibility of resin [1] with other resins willbe poor, and the weather resistance of the cured product of thecomposition will be poor.

The other copolymerizable vinylic monomers are not also specificallydefined, and include, for example, methyl (meth)acrylate, ethyl(meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate,tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate,3,3,5-trimethylcyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,isobornyl (meth)acrylate, stearyl (meth)acrylate, benzyl (meth)acrylate,cyclohexyl (meth)acrylate, trifluoroethyl (meth)acrylate,pentafluoropropyl (meth)acrylate, as well as unsaturatedpolycarboxylates such as diesters or half-esters of unsaturatedpolycarboxylic acids (maleic acid, fumaric acid, itaconic acid, etc.)with linear or branched alcohols having from 1 to 20 carbon atoms;aromatic hydrocarbon-based vinyl compounds such as styrene,α-methylstyrene, chlorostyrene, sodium styrenesulfonate, etc.; vinylesters and allyl compounds such as vinyl acetate, vinyl propionate,diallyl phthalate, etc.; nitrile group-having vinyl compounds such as(meth)acrylonitrile, etc.; silane compounds such asγ-(meth)acryloxypropyltrimethoxysilane,γ-(meth)acryloxypropyltriethoxysilane, γ-(meth)acryloxypropyltrisilanol,γ-(meth)acryloxypropylmethyldimethoxysilane, vinyltrimethoxysilane,vinyltriethoxysilane, 2-styrylethyltrimethoxysilane,allyltriethoxysilane, etc.; basic nitrogen atom-containing vinylcompounds such as dimethylaminoethyl (meth)acrylate, dimethylaminoethyl(meth)acrylate, diethylaminoethyl (meth)acrylate, vinylpyridine,aminoethyl vinyl ether, etc.; amido group-having vinyl compounds such as(meth)acrylamide, itaconic acid diamide, α-ethyl(meth)acrylamide,crotonamide, maleic acid diamide, fumaric acid diamide,N-vinylpyrrolidone, N-butoxymethyl(meth)acrylamide,N,N-dimethylacrylamide, N-methylacrylamide, acryloylmorpholine, etc.;other vinyl compounds such as vinyl methyl ether, vinyl chloride,vinylidene chloride, chloroprene, propylene, butadiene, isoprene,maleimide, N-vinylimidazole, etc.

For producing resin [1], preferred is a solution polymerization methodusing a peroxide-type radical initiator such as t-butyl peroxyacetate orthe like, or using an azo-type radical initiator such asazobisisobutyronitrile or the like, since resin [1] is produced easilyin the method.

If desired, in the method, a chain transfer agent may be used forcontrolling the molecular weight of the polymers produced. The chaintransfer agent includes, for example, n-dodecylmercaptan,t-dodecylmercaptan, n-butylmercaptan, γ-mercaptopropyltrimethoxysilane,γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldimethoxysilane,γ-mercaptopropylmethyldiethoxysilane, etc.

The polymerization solvent to be used in the solution polymerization isnot specifically defined, so far as it is inactive to thepolymerization. For example, employable are inactive solvents such ashydrocarbons (toluene, xylene, n-hexane, cyclohexane, etc.), acetates(ethyl acetate, butyl acetate, etc.), alcohols (methanol, ethanol,isopropanol, n-butyl alcohol, etc.), ethers (ethyl cellosolve, butylcellosolve, cellosolve acetate, etc.), ketones (methyl ethyl ketone,ethyl acetacetate, acetylacetone, diacetonealcohol, methyl isobutylketone, acetone, etc.).

The number-average molecular weight of resin [1] is preferably from2,000 to 20,000, more preferably from 2,500 to 15,000, in view of theexpected physical properties, such as durability and others, of thecured films to be formed from the curable composition of the invention.

The epoxy equivalent of resin [1] is preferably from 200 to 2,000 g/mol,more preferably from 250 to 1,000 g/mol, even more preferably from 300to 750 g/mol, in view of the curability of the composition and of theweather resistance as well as the final appearance of the cured films ofthe composition.

[Resin [2] (resin having both epoxy and hydroxyl groups)]

The epoxy equivalent of resin [2] is preferably from 200 to 2,000 g/mol,more preferably from 250 to 1,000 g/mol, even more preferably from 300to 750 g/mol. If the epoxy equivalent is smaller than 200 g/mol, thecoating film from the composition will be too hard, and its weatherresistance is therefore poor. If, however, the epoxy equivalent islarger than 2,000 g/mol, the thermal curability of the composition willbe poor and, in addition, the final appearance and the impact resistanceof the coating films from the composition will also be poor.

The hydroxyl equivalent of resin [2] is preferably not smaller than 400g/mol, more preferably not smaller than 450 g/mol, even more preferablyfrom 500 to 3,000 g/mol. If the hydroxyl equivalent is smaller than 400g/mol, the waterproofness and the acid resistance of the coating filmsfrom the composition will be poor.

The number-average molecular weight of resin [2] is preferably from2,000 to 20,000, more preferably from 2,500 to 10,000. If thenumber-average molecular weight is smaller than 2,000, the mechanicalproperties and also the waterproofness of the coating films from thecomposition will be poor. However, if it is larger than 20,000, theviscosity of the composition will be too high, resulting in that thesolid concentration of the composition must be lowered prior to usingthe composition for coating.

Resin [2] comprises, for example, units from hydroxyl group-havingmonomers, units from epoxy group-having vinylic monomers such as thosenoted above, and units from other copolymerizable vinylic monomers,etc.; and it may be produced in solution polymerization using a radicalinitiator.

The hydroxyl group-having monomers are not specifically defined,including, for example, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl(meth)acrylate, 2-hydroxyethyl vinyl ether, N-methylol(meth)acrylamide,4-hydroxystyrene-vinyltoluene, Toa Synthetic Chemical's Aronics 5700,4-hydroxystyrene, Nippon Shokubai Kagaku's HE-10, HE-20, HP-1 and HP-20(these are all hydroxyl-terminated acrylate oligomers), Nippon Oils &Fats' Blemmer PP series (polypropylene glycol methacrylates), Blemmer PEseries (polyethylene glycol monomethacrylates), Blemmer PEP series(polyethylene glycol polypropylene glycol methacrylates), Blemmer AP-400(polypropylene glycol monoacrylate), Blemmer AE-350 (polyethylene glycolmonoacrylate), Blemmer NKH-5050 (polypropylene glycol polytrimethylenemonoacrylate), and Blemmer GLM (glycerol monomethacrylate), as well asε-caprolactone-modified, copolymerizable hydroxyalkylvinylic compoundsas obtained through reaction of hydroxyl group-having vinylic compoundsand ε-caprolactone.

These hydroxyl group-having vinylic monomers may be used either singlyor as combined.

The amount of the hydroxyl group-having vinylic monomers to be used inproducing resin [2] is preferably from 5 to 50%, more preferably from 7to 40% of the total amount of the comonomers for resin [2]. If theamount of the monomers used is smaller than 5%, the resultingcomposition could not have good curability. However, if it is largerthan 50%, the waterproofness and the acid resistance of the coatingfilms from the composition will be poor.

[Resin [3] (resin having both epoxy and hydrolyzable silyl groups]

Resin [3] is a vinylic copolymer, of which the main chain issubstantially a vinylic copolymer chain. The vinylic copolymer of resin[3] has, in one molecule, at least one hydrolyzable silyl group of thefollowing general formula (I) at the terminals of the main chain and/orin the side chains, and at least one epoxy group at the terminals of themain chain and/or in the side chains, in which the silyl group is bondedto the carbon atom in the molecule and its conception includes silanolgroups.

wherein R¹ represents a hydrogen atom, or an alkyl group having from 1to 10 carbon atoms; R² represents a hydrogen atom, or a monovalenthydrocarbon group selected from an alkyl group having from 1 to 10carbon atoms, an aryl group and an aralkyl group; and a represents aninteger of from 0 to 2.

Since resin [3] is such a vinylic copolymer, of which the main chain issubstantially a vinylic copolymer chain, the coating films from thecurable composition comprising resin [3] have good weather resistanceand chemical resistance. In addition, since resin [3] contains at leastone hydrolyzable silyl group as bonded to the carbon atom therein, thecoating films from the composition comprising it have goodwaterproofness, alkali resistance and acid resistance.

The component (A) shall have at least one hydrolyzable silyl group offormula (I) in one molecule, but preferably from 2 to 10 suchhydrolyzable silyl groups, in view of the scratch resistance and thesolvent resistance of the coating films from the composition.

In formula (I), R¹ represents a hydrogen atom or an alkyl group havingfrom 1 to 10 carbon atoms, but is preferably an alkyl group having from1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, i-propyl, n-butyl,i-butyl or t-butyl group. If the number of carbon atoms constituting thealkyl group is larger than 10, the reactivity of the hydrolyzable silylgroup will be low. If R¹ is any other group except alkyl groups, forexample, if it is a phenyl group, a benzyl group or the like, such othergroups are unfavorable since the reactivity of the hydrolyzable silylgroup is also low.

In formula (I), R² may be a hydrogen atom, or an alkyl group having from1 to 10 carbon atoms, but is preferably a monovalent hydrocarbon groupselected from an alkyl group having from 1 to 4 carbon atoms, of whichthe specific examples are the same as those mentioned hereinabove forR¹, an aryl group having from 6 to 25 carbon atoms, such as a phenylgroup, etc., and an aralkyl group having from 7 to 12 carbon atoms suchas a benzyl group, etc. Of those, preferred is an alkyl group, since thecurability of the composition to be obtained herein is good.

The epoxy equivalent of resin [3] is from 200 to 2,000 g/mol, preferablyfrom 250 to 1,000 g/mol, more preferably from 300 to 750 g/mol. If theepoxy equivalent is smaller than 200 g/mol, the coating films from thecomposition will be too hard and therefore have poor weather resistance.On the other hand, if the epoxy equivalent is larger than 3,000 g/mol,the thermal curability of the composition is poor, and, in addition, thescratch resistance and the final appearance of the coating films fromthe composition will be poor.

The hydrolyzable silyl equivalent of the vinylic copolymer (resin [3])is preferably not smaller than 500 g/liter, more preferably not smallerthan 600 g/liter, even more preferably not smaller than 700 g/liter,from the viewpoint that the curable composition comprising the copolymerhas good thermal curability and that the coating films from thecomposition have good acid resistance and goodscratch resistance. If,however, the hydrolyzable silyl equivalent of the copolymer is smallerthan 500 g/liter, the inner stress of the coating films from thecomposition will be large, and therefore the weather resistance thereofwill be poor.

The resin [3] may comprise, for example, units from hydrolyzable silylgroup-having vinylic monomers, units from epoxy group-having vinylicmonomers such as those mentioned above, and units from othercopolymerizable vinylic monomers such as those mentioned above, etc.,and it may be produced by solution polymerization using a radicalinitiator.

The hydrolyzable silyl group-having vinylic monomers include, forexample, the following:

Compounds of a general formula (III):

wherein R¹, R² and a have the same meanings as above; and R⁵ representsa hydrogen atom or a methyl group, for example, the following:

Compounds of a general formula (IV):

for example, the following:

Compounds of a general formula (V):

for example, the following:

CH₂=CH—CH₂OCO(o—C₆H₄)COO(CH₂)₃Si(OCH₃)₃.

CH₂=CH—CH₂OCO(o—C₆H₄)COO(CH₂)₃Si(CH₃)(OCH₃)₂.

Compounds of a general formula (VII):

wherein R¹, R², R⁵ and a have the same meanings as above; and prepresents an integer of from 0 to 22, for example, the following:

They further include (meth)acrylates having the hydrolyzable silyl groupof formula (III) as bonded to the terminal via urethane bonding orsiloxane bonding. These monomers may be used either singly or ascombined. Of those, preferred are compounds of formula (V), as they areeasy to handle and are inexpensive and they do not give any sideproducts in polymerization.

The amount of the hydrolyzable silyl group-having vinylic monomers to beused in producing resin [3] is preferably from 5 to 60% (by weight—thesame shall apply hereunder), more preferably from 10 to 50% of the totalamount of the comonomers for resin [3]. If the amount of thehydrolyzable silyl group-having monomers used is smaller than 5%, thecoating films from the curable composition obtained will have poor acidresistance. However, if the amount is larger than 60%, the storagestability of the curable composition will be poor.

The number-average molecular weight of resin [3] is preferably from2,000 to 20,000, more preferably from 2,500 to 15,000, in view of theexpected physical properties, such as durability and others, of thecured films to be formed from the curable composition.

[Resin [4] (resin having all epoxy, hydrolyzable silyl and hydroxylgroups)]

Resin [4] comprises, for example, units from epoxy group-having vinylicmonomers such as those mentioned above, units from hydroxyl group-havingvinylic monomers such as those mentioned above, units from hydrolyzablesilyl group-having vinylic monomers such as those mentioned above, andunits from any other copolymerizable vinylic monomers such as thosementioned above, etc., and it may be produced in solution polymerizationusing a radical initiator.

In resin [4], the molar ratio of alcoholic hydroxyl groups tohydrolyzable silyl groups (alcoholic hydroxyl groups/hydrolyzable silylgroups) preferably falls between 0.0 and 10, more preferably between 0.1and 7.5, even more preferably between 0.2 and 4.0, from the viewpointthat the curable composition to be obtained has good thermal curabilityand that the coating films from the composition have good acidresistance, good weather resistance and good waterproofness.

In order to make resin [4] have the molar ratio falling within thedefined range, for example, the amount of the hydrolyzable silylgroup-having vinylic monomers and that of the alcoholic hydroxylgroup-having vinylic monomers to be used in producing resin [4] may besuitably controlled.

The number-average molecular weight of resin [4] is preferably from2,000 to 20,000, more preferably from 2,500 to 10,000. If the molecularweight is smaller than 2,000, the mechanical properties and also thewaterproofness of the coating films from the composition obtained willbe poor. However, if it is larger than 20,000, the viscosity of thecomposition will be too high, resulting in that the solid concentrationof the composition must be lowered prior to using the composition forcoating.

Resin [3] and resin [4] are preferred to resin [1] and resin [2], sincethe curable composition comprising the former has better thermalcurability and since the coating films from the composition comprisingthe former have better scratch resistance and better weather resistance.

Component (B)

The component (B) for use in the invention is a compound having at least2 carboxyl groups, which includes, for example, carboxyl group-havingoligomer compounds to be prepared through half-esterification of polyolcompounds and acid anhydrides, as well as carboxyl group-having vinyliccopolymers.

The compounds for the component (B) may be used either singly or ascombined.

The carboxyl group-having oligomer compound is prepared throughhalf-esterification of a polyol compound and an acid anhydride, and hasat least 2 carboxyl groups in one molecule. In view of the weatherresistance, the acid resistance and the recoating adhesiveness of thecoating films from the composition of the invention, the oligomercompound is preferably one having at least 2 carboxyl groups in onemolecule (hereinafter referred to as “carboxylic acid oligomer”), whichis prepared through half-esterification of a polyol compound having atleast 2, but preferably from 2 to 10 hydroxyl groups in one molecule,with an acid anhydride.

The polyols having at least 2 hydroxyl groups in one molecule, which arefor producing the carboxylic acid oligomers for use in the invention,include, for example, polyalcohols such as ethylene glycol, 1,2- and1,3-propylene glycols, 1,3-butane-diol, 1,4-butane-diol,2,3-butane-diol, 1,6-hexane-diol, diethylene glycol, pentane-diol,dimethylbutane-diol, hydrogenated bisphenol A, glycerin, sorbitol,neopentyl glycol, 1,3-octane-diol, 1,4-cyclohexane-dimethanol,2-methyl-1,3-propane-diol, 1,2,6-hexane-triol, 1,2,4-butane-triol,trimethylolethane, trimethylolpropane, pentaerythritol, quinitol,mannitol, trishydroxyethyl isocyanurate, dipentaerythritol,trishydroxymethylethane, etc.; ring-cleaved adducts of lactonecompounds, such as γ-butyrolactone, ε-caprolactone or the like, to thosepolyalcohols; alcohol-rich adducts of isocyanate compounds, such astolylene diisocyanate, diphenylmethane diisocyanate, hexamethylenediisocyanate, isophorone diisocyanate or the like, to thosepolyalcohols; alcohol-rich adducts of vinyl ether compounds, such asethylene glycol divinyl ether, polyethylene glycol divinyl ether,butane-diol divinyl ether, pentane-diol divinyl ether, hexane-dioldivinyl ether, 1,4-cyclohexane-dimethanol divinyl ether, to thosepolyalcohols; alcohol-rich condensates of those polyalcohols withalkoxysilicone compounds, such as KR-213, KR-217, KR-9218 (all tradenames of products of Shin-etsu Chemical Industry), etc.

As preferred acid anhydrides to be reacted with those polyols, forexample, mentioned are hexahydrophthalic anhydride, phthalic anhydride,methylhexahydrophthalic anhydride, tetrahydrophthalic anhydride,trimellitic anhydride, etc.

Suitably controlling the ratio of the polyol to the acid anhydride to bereacted therewith will give hydroxyl group-containing carboxylic acidoligomers.

The molecular weight of the carboxyl group-having oligomer compounds ispreferably not larger than 2,000, more preferably from 100 to 1,800.

The carboxyl group-having vinylic copolymers may be prepared, forexample, in solution polymerization of carboxyl group-having, vinylicpolymerizable compounds and any other polymerizable vinylic monomerssuch as those mentioned above, in the presence of a radical initiator.Alternatively, they may also be prepared through radical polymerizationof acid anhydride group-having, radical-polymerizable monomers and anyother copolymerizable vinylic monomers such as those mentioned above togive copolymers, followed by half-esterification of the resultingcopolymers at the acid anhydride groups therein.

The carboxyl group-having, vinylic polymerizable compounds include, forexample, α,β-ethylenic unsaturated carboxylic acids such as acrylicacid, methacrylic acid, itaconic acid, maleic acid, etc.; as well ashalf esters of anhydrides of such acids with linear or branched alcoholshaving from 1 to 20 carbon atoms. The acid anhydride group-having,radical-polymerizable monomers include, for example, itaconic anhydride,maleic anhydride, citraconic anhydride, etc.

The amount of the carboxyl group-having, vinylic polymerizable compoundsand the acid anhydride group-having, radical-polymerizable monomers tobe used for producing the polymers is preferably from 10 to 50% byweight, more preferably from 15 to 40% by weight of all monomers used.

The half-esterifying agent for the half-esterification may be an alcoholhaving a low molecular weight, including, for example, methanol,ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, t-butanol,methyl cellosolve, ethyl cellosolve, dimethylaminoethanol, acetol, allylalcohol, propargyl alcohol, etc. Especially preferred are acetol, allylalcohol, propargyl alcohol, ethanol, and methanol.

The half-esterification may be effected in any ordinary manner, at atemperature falling between room temperature and 120° C. and in thepresence of a catalyst. The catalyst includes, for example, tertiaryamines (e.g., triethylamine, tributylamine, etc.), and quaternaryammonium salts (e.g., benzyltrimethylammonium chloride,benzyltrimethylammonium bromide, benzyltributylammonium chloride,benzyltributylammonium bromide, etc.).

The carboxyl group-having compound for the component (B) as prepared inthe manner noted above preferably has a number average molecular weightof from 1,000 to 20,000, more preferably from 2,000 to 10,000. If themolecular weight is smaller than 1,000, the mechanical properties of thecoating films from the composition obtained will be poor. However, if itis larger than 20,000, the viscosity of the composition will be toohigh, resulting in that the solid concentration of the composition mustbe lowered prior to using the composition for coating.

The compound must have at least 2 carboxyl groups in one molecule. Ifthe number of the carboxyl groups in the compound is smaller than 2, thecomposition could not have good curability.

The amount of the component (B) to be in the composition is from 0.001to 100 parts by weight, relative to 100 parts by weight of the component(A). If the amount of the component (B) is larger than 100 parts byweight, there may occur a problem that the waterproofness of the coatingfilms from the composition will be poor and, in addition, the storagestability of the composition for coating will be poor. If, however, theamount is smaller than 0.001 parts by weight, there may occur anotherproblem that the curability of the composition will be poor. Thepreferred range of the amount of the component (B) falls between 0.01and 80 parts by weight, more preferably between 0.1 and 50 parts byweight.

The molar ratio of the epoxy group in the vinylic copolymer (A) to thecarboxyl group in the component (B) is preferably such that the molarnumber of the epoxy group relative to one mol of the carboxyl group(epoxy group/carboxyl group) is from 0.2 to 5.0, more preferably from0.2 to 4.0, even more preferably from 0.5 to 3.0, in order that thecurable composition could have good thermal curability and that thecoating films from the composition could have good acid resistance, goodweather resistance and good waterproofness.

For the component (B), carboxyl group-having oligomer compounds arepreferred to carboxyl group-having resins from the viewpoint that thecurable composition obtained could have better thermal curability andthat the coating films from the composition could have better scratchresistance and better recoating adhesiveness.

Component (C)

The organic solvent for the component (C) for use in the invention maybe selected from glycol monoalkyl ethers, vinyl ethers and cyclicethers. One or more of these may be used either singly or as combined.

The glycol monoalkyl ethers include, for example, ethylene glycolmonomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether,ethylene glycol monopropyl ether, ethylene glycol monobutyl ether,ethylene glycol phenyl ether, ethylene glycol hexyl ether, ethyleneglycol monomethoxy ether, propylene glycol monomethyl ether, propyleneglycol monoethyl ether, propylene glycol monopropyl ether, diethyleneglycol monomethyl ether, diethylene glycol monoethyl ether, etc.

The vinyl ethers include, for example, methyl vinyl ether, ethyl vinylether, propyl vinyl ether, butyl vinyl ether, 3,4-dihydro-2H-pyran,3,4-dihydrofuran, 3,4-dihydro-2-methoxy-2H-pyran, etc.

The cyclic ethers include, for example, tetrahydrofuran,tetrahydropyran, diethylene oxide, etc.

The glycol monoalkyl ethers are preferred, since they smell little inthe coating composition and since their ability to improve the storagestability of the composition is great.

The component (C) further comprises any of monoalkyl alcohol compoundsand compounds capable of being hydrolyzed through reaction with water togive alcohols (dehydrating agents). One or both of these compounds maybe used either singly or as combined.

The monoalkyl alcohol compounds include, for example, methanol, ethanol,n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, etc.

The compounds capable of being hydrolyzed through reaction with water togive alcohols may be hydrolyzable ester compounds, including, forexample, trimethyl orthoformate, triethyl orthoformate, trimethylorthoacetate, triethyl orthoacetate, as well as tetraalkyl silicatessuch as tetramethyl silicate, tetraethyl silicate or the like, and evencondensates of such tetraalkyl silicates and their analogues, etc. Thesemay be used either singly or as combined.

The amount of the solvent and that of the dehydrating agent for thecomponent (C) each may be from 1.0 to 50 parts by weight, preferablyfrom 5.0 to 30 parts by weight, relative to 100 parts by weight of thetotal solid resin content of the composition.

If the amounts of those solvent and dehydrating agent each are smallerthan 1.0 part by weight, the storage stability of the composition, towhich the invention is directed, will be bad. However, if they arelarger than 50 parts by weight each, the vaporizing rate of the solventfrom the coated composition is difficult to control, thereby oftenresulting in that the final appearance of the coating films formed willbe poor.

If the amount of the dehydrating agent to be in the curable compositionis too large, the coating films from the composition will have defectssuch as pin holes, etc. Therefore, the amount of the dehydrating agentshall be not larger than 50 parts by weight, preferably not larger than30 parts by weight, more preferably not larger than 20 parts by weight,relative to 100 parts by weight of the component (A).

The component (C) may be previously in the components (A) and (B) whilethey are produced. However, in view of the storage stability of thecomposition, it is desirable that the component (C) is added to themixture of the components (A) and (B).

Component (D)

The curing catalyst for the component (D) for use in the invention isnot specifically defined, so far as it is usable as a curing catalystfor hydrolyzable silyl group-having compounds, or usable inesterification of acids with epoxy compounds.

As specific examples of the component (D), for example, mentioned areorganic tin compounds such as dibutyl tin dilaurate, dibutyl tindimaleate, dioctyl tin dilaurate, dioctyl tin dimaleate, tin octylate,etc.; phosphoric acid or phosphates such as phosphoric acid, monomethylphosphate, monoethyl phosphate, monobutyl phosphate, monooctylphosphate, monodecyl phosphate, dimethyl phosphate, diethyl phosphate,dibutyl phosphate, dioctyl phosphate, didecyl phosphate, etc.; adductsof phosphoric acid and/or monophosphates to epoxy compounds, such aspropylene oxide, butylene oxide, cyclohexene oxide, glycidylmethacrylate, glycidol, acrylglycidyl ether,γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane,γ-glycidoxypropylmethyldimethoxysilane, Yuka Shell Epoxy's Cardula E,Yuka Shell Epoxy's Epikote 828, Epikote 1001, etc.; organic titanatecompounds; organic aluminium compounds; organic zinc compounds;carboxylic acid compounds (organic carboxylic acid compounds) such asmaleic acid, adipic acid, azelaic acid, sebacic acid, itaconic acid,citric acid, succinic acid, phthalic acid, trimellitic acid,pyromellitic acid, etc., and their anhydrides; sulfonic acid compounds(organic sulfonic acid compounds) such as dodecylbenzenesulfonic acid,paratoluenesulfonic acid, 1-naphthalenesulfonic acid,2-naphthalenesulfonic acid, etc., and those sulfonic acid compounds asblocked with nitrogen-containing compounds (e.g., 1-amino-2-propanol,monoethanolamine, diethanolamine, 2-(methylamino)ethanol,2-dimethylethanolamine, 2-amino-2-methyl-1-propanol, diisopropanolamine,3-aminopropanol, 2-methylamino-2-methylpropanol, morpholine,oxazolidine, 4,4-dimethyloxazolidine, 3,4,4-trimethyloxazolidine, etc.)(these are reaction products of acids and amines) (for example, KingIndustries' NACURE 5225, NACURE 5543, NACURE 5925, etc.); amines such ashexylamine, di-2-ethylhexylamine, N, N-dimethyldodecylamine,dodecylamine, DABCO, DBU, morpholine, diisopropanolamine, etc.; reactionproducts of those amines with acidic phosphates; alkaline compounds suchas sodium hydroxide, potassium hydroxide, etc.; quaternary ammoniumsalts such as benzyltriethylammonium chloride or bromide,tetrabutylammonium chloride or bromide, etc.; phosphonium salts, etc.One or more of these curing catalysts may be used either singly or ascombined.

Of the curing catalysts noted above, preferred are sulfonic acidcompounds as blocked with nitrogen-containing compounds, since thecurability of the composition being baked and the storage stability ofthe composition at room temperature are well balanced. For those, thenitrogen-containing compound is preferably at least one of primary orsecondary amine compounds having 1 or 2 hydroxyl groups in one molecule(e.g., 2-amino-2-methyl-1-propanol, diisopropanolamine, etc.),morpholine and oxazolidine. The preferred curing catalysts may becombined with any of organic tin compounds, phosphoric acid andphosphates such as those mentioned above.

The equivalent ratio of the sulfonic acid compound to thenitrogen-containing compound preferably is from 1/0.75 to 1/3.0, morepreferably from 1/1.0 to 1/2.0. If the amount of the nitrogen-containingcompound is smaller than 0.75 in terms of the equivalent ratio, thestorage stability of the composition at room temperature will be poor,and the outward appearance of the coating films from the compositionwill be poor. If, however, it is larger than 3.0, the curability of thecomposition being baked will be poor, and the coating films from thecomposition will be greatly yellowed.

Component (E)

The hydroxyl group-having compound for the component (E) does not have ahydrolyzable silyl group. The compound is not always needed to be avinylic copolymer. However, in view of the durability of the coatingfilms from the composition, it is desirable that the compound for thecomponent (E) is a hydroxyl group-having copolymer of vinylic monomers(this is hereinafter referred to as “acrylic polyol”).

The acrylic polyol may be prepared, for example, by copolymerizinghydroxyl group-having vinyl monomers with any other copolymerizablevinylic monomers.

The comonomers of hydroxyl group-having vinyl monomers are notspecifically defined, including, for example, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl(meth)acrylate, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl vinylether, N-methylol(meth)acrylamide, 4-hydroxystyrene-vinyltoluene, ToaSynthetic Chemical's Aronics 5700, 4-hydroxystyrene, Nippon ShokubaiKagaku's HE-10, HE-20, HP-1 and HP-20 (these are all hydroxyl-terminatedacrylate oligomers), Nippon Oils & Fats' Blemmer PP series(polypropylene glycol methacrylates), Blemmer PE series (polyethyleneglycol monomethacrylates), Blemmer PEP series (polyethylene glycolpolypropylene glycol methacrylates), Blemmer AP-400 (polypropyleneglycol monoacrylate), Blemmer AE-350 (polyethylene glycol monoacrylate),Blemmer NKH-5050 (polypropylene glycol polytrimethylene monoacrylate),and Blemmer GLM (glycerol monomethacrylate), as well asε-caprolactone-modified, copolymerizable hydroxyalkylvinylic compoundsas obtained through reaction of hydroxyl group-having vinylic compoundsand ε-caprolactone, and Daicel Chemical Industry's HEAC-1 (this has acarbonate structure), etc.

These hydroxyl group-having vinylic monomers may be used either singlyor as combined.

The other vinylic monomers copolymerizable with those hydroxylgroup-having vinylic monomers are not specifically defined, and theirexamples include methyl (meth)acrylate, ethyl (meth)acrylate, butyl(meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate,cyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate,2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, stearyl(meth)acrylate, benzyl (meth)acrylate, cyclohexyl (meth)acrylate,trifluoroethyl (meth)acrylate, pentafluoropropyl (meth)acrylate, as wellas unsaturated polycarboxylates such as diesters or half-esters ofunsaturated polycarboxylic acids (maleic acid, fumaric acid, itaconicacid, etc.) with linear or branched alcohols having from 1 to 20 carbonatoms; aromatic hydrocarbon-based vinyl compounds such as styrene,α-methylstyrene, chlorostyrene, sodium styrenesulfonate, etc.; vinylesters and allyl compounds such as vinyl acetate, vinyl propionate,diallyl phthalate, etc.; nitrile group-having vinyl compounds such as(meth)acrylonitrile, etc.; epoxy group-having vinyl compounds such asglycidyl (meth)acrylate, etc.; basic nitrogen atom-containing vinylcompounds such as dimethylaminoethyl (meth)acrylate, dimethylaminoethyl(meth)acrylate, diethylaminoethyl (meth)acrylate, vinylpyridine,aminoethyl vinyl ether, etc.; amido group-having vinyl compounds such as(meth)acrylamide, itaconic acid diamide, α-ethyl(meth)acrylamide,crotonamide, maleic acid diamide, fumaric acid diamide,N-vinylpyrrolidone, N-butoxymethyl(meth)acrylamide,N,N-dimethylacrylamide, N-methylacrylamide, acryloylmorpholine, etc.

One or more of those vinylic monomers copolymerizable with hydroxylgroup-having vinylic monomers may be used either singly or as combined.

The acrylic polyol may have segments comprising urethane bonding orsiloxane bonding, in its main chain in an amount of smaller than 50%.

The acrylic polyol is preferably prepared in solution polymerizationusing a radical initiator. In the solution polymerization, optionallyused is a chain transfer agent such as n-dodecylmercaptan by which themolecular weight of the polymer formed could be controlled.

As the polymerization solvent, usable is a non-reactive solvent, bywhich, however, the present invention is not restricted.

One or more acrylic polyols may be used either singly or as combined.

As specific examples of the hydroxyl group-having compound for thecomponent (E), which is not a vinylic copolymer, for example, mentionedare organic polyols such as polycaprolactone-polyol,polyvalerolactone-polyol, polyhexamethylene carbonate-polyol, etc.

The acrylic polyol is preferably a non-aqueous dispersed polymer, inview of the breaking stress and elongation of the coating films from thecomposition and of the easiness in controlling the rheology of thecomposition.

The non-aqueous dispersed polymer is meant to indicate a polymer asstably dispersed in an organic medium, as so written in literature suchas “Dispersion Polymerization in organic Media” by K. E. J. Barrett(John Wiley & Sons, London, 1975). The polymer is composed of (1) a coresite and (2) an arm site, in which the both sites are bonded to eachother via covalent bonding, for example, through reaction of thecarboxylic acid group and the epoxy group therein.

The core site (1) is of a macromolecular polymer having a number-averagemolecular weight of from 15,000 to 300,000 and dispersed in an organicmedium; while the arm site (2) is of a polymer which is soluble in anorganic solvent by itself and which is a stabilizer to form athree-dimensional barrier. The arm site (2) forms a macromer chain tobond to the core site (1).

The core site (1) is of a copolymer of vinylic monomers. The monomersare not specifically defined, and their examples include acrylic acid,methacrylic acid, and their alkyl esters, hydroxyalkyl esters, allylesters and glycidyl esters, as well as styrene, acrylonitrile, etc.

The arm site (2) bonding to the core site (1) accounts for from 10 to90%, preferably from 20 to 50% of the dispersed polymer. If the amountof the arm site (2) is larger than 90% of the dispersed polymer, curedproducts with good durability are difficult to obtain. If, on thecontrary, the amount is smaller than 10%, the viscosity of the dispersedpolymer will be too high, or the dispersed polymer will have poorstability and will give precipitates.

The organic solvent-soluble polymer for the arm site may comprise from 5to 30 parts by weight, preferably from 5 to 25 parts by weight of atleast one, hydroxyl group-having vinylic monomer, and from 70 to 95parts by weight, preferably from 75 to 95 parts by weight of at leastone other vinylic monomer not having a hydroxyl group. If the amount ofthe hydroxyl group-having vinylic monomer is smaller than 5 parts byweight, the curability of the composition formed will be poor. If, onthe contrary, the amount is larger than 30 parts by weight, thesolubility of the polymer in organic solvents will be low, and stabilityof the dispersed polymer will be poor.

It is desirable that the component (E) is added to the composition whenthe component (A) in the composition is resin [3] or resin [4]. Wherethe hydroxyl group-having compound of the component (E) to be added tothe composition is not a non-aqueous dispersed polymer, it is desirablethat the amount of the component (E) to be added is so controlled thatthe number of the alcoholic hydroxyl group in the component (E) is lessthan 0.1 per one R¹O—Si group in the component (A) (resin [3], resin[4]).

Where the hydroxyl group-having compound of the component (E) to beadded to the composition is a non-aqueous dispersed polymer, it isdesirable that the amount of the component (E) to be added is socontrolled that the number of the alcoholic hydroxyl group in the armsite in the component (E) is less than 0.2, more preferably less than0.1, per one R¹O—Si group in the component (A) (resin [3], resin [4]).

In any case, if the alcoholic hydroxyl group in the component (E) addedis too much, the acid resistance and the waterproofness of the coatingfilms from the composition will be poor.

Where the component (E) is not a non-aqueous dispersed polymer, it isdesirable that the number-average molecular weight of the compound ofthe component (E) falls between 1,000 and 25,000, more preferablybetween 1,000 and 15,000. If the number-average molecular weight of thecompound is smaller than 1,000, the weather resistance and thewaterproofness of the coating films from the composition will be poor.If, on the contrary, it is larger than 25,000, the compatibility of theconstituent components will be poor.

Where the component (E) is a non-aqueous dispersed polymer, it is alsodesirable that the number-average molecular weight of the organicsolvent-soluble polymer that constitutes the non-aqueous dispersedpolymer is from 1,000 to 25,000, more preferably from 1,000 to 15,000.If the number-average molecular weight of the polymer is smaller than1,000, the stability of the dispersed polymer will be poor. If, on thecontrary, it is larger than 25,000, the polymer forming the arm sitecould hardly dissolve in organic solvents.

The amount of the component (E) in the composition may be from 0 to 80parts by weight relative to 100 parts by weight of the total solidcontent of the components (A) and (B) therein. If the amount of thecomponent (E) is larger than 80 parts by weight, the acid resistance andthe waterproofness of the coating films from the composition will bepoor. Preferably, the amount of the component (E) is from 0 to 60 partsby weight, more preferably from 0 to 50 parts by weight, even morepreferably from 0.001 to 50 parts by weight.

Component (F)

The curable composition of the invention may further contain an aminoresin as the component (F), in addition to the components (A) to (E)noted above, for the purpose of further improving the curability of thecomposition and improving the outward appearance of the coating filmsfrom the composition.

The amount of the amino resin for the component (F) may be up to 30parts by weight, preferably up to 15 parts by weight, more preferably upto 5 parts by weight, relative to 100 parts by weight of the total solidresin content of the components (A), (B) and (E). If the amount of theamino resin (F) is larger than 30 parts by weight, the acid resistanceof the coating films from the composition will be poor. In order to moreeffectively attain its effect, the amount of the component (F) to beadded is desirably 1 part by weight or more.

As examples of the amino resin (F), mentioned are amino resins(methylolated amino resins such as melamine resins, urea resins,guanamine resins, etc.), which may be prepared through reaction of anamino component, such as melamine, urea, benzoguanamine, glycol urea,acetoguanamine, dicyandiamide or the like, and an aldehyde componentsuch as formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde orthe like.

Of those amino resins, preferred are melamine resins, since the finalappearance of the coating films from the composition is good and sincethe curability of the composition is good.

The amino resins (e.g., methylolated amino resins) may be etherifiedwith alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol,iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, 2-ethylbutanol,2-ethylhexanol, etc.

Specific examples of the amino resin (F) include n-butylated melamineresins such as Mitsui Toatsu Chemical's Uban 20SE, Uban 20SE-60, Uban128, Uban 220, Uban 225, Uban 20SB, Uban 20SE-60, Uban 21R, Uban 22R,Uban 122, Uban 28-60, Uban 20HS, Uban2028, Uban202, Uban 120, etc.;isobutylatedmelamine resins such as Uban 62, Uban 69-1, Uban 169, Uban2061, etc.; butylated urea resins such as Uban 10S-60, Uban 10R, etc.;melamine resins such as Mitsui Cytec's Cymel 303, Cymel 232, Cymel 370,Cymel 325, Cymel 236, Cymel 738, Cymel 771, Cymel 327, Cymel 703, Cymel701, Cymel 266, Cymel 267, Cymel 285, Cymel 235, Cymel 238, Cymel 1141,Cymel 272, Cymel 254, Cymel 202, Cymel 1156, Cymel 1158, Cymel 300,Cymel 301, Cymel 350, Cymel 736, etc. Of those, preferred arealkyl-etherified melamine resins such as Cymel 235, Cymel 238, Cymel1158, etc., in view of the curability of the composition.

Others

For the curable composition of the invention, further usable aresolvents, in which both the components (A) and (B) are soluble or stablydispersible. The solvents may be the same as those used in producing thevinylic copolymer (A). As typical examples of such solvents, mentionedare hydrocarbons such as toluene, xylene, cyclohexane, n-hexane, octane,etc.; alcohols such as methanol, ethanol, iso-propanol, n-butanol,iso-butanol, sec-butanol, t-butanol, etc.; esters such as methylacetate, ethyl acetate, butyl acetate, etc.; ketones such as acetone,methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc.

The solvents used in polymerization to form the component (A) may bedirectly used as those for the components (A) and (B).

The amount of the solvent to be used is not specifically defined.However, if too much solvent is used, the coating films from thecomposition obtained will have defects, for example, the films will befoamed. Therefore, the amount of the solvent to be used is generally notlarger than 70 parts by weight, preferably not larger than 50 parts byweight, more preferably not larger than 20 parts by weight, relative to100 parts by weight of the component (A).

Weather resistance improvers such as UV absorbents, light stabilizersand the like may be added to the curable composition for top coating ofthe invention, to thereby further improve the weather resistance of thecoating films from the composition. In particular, adding both UVabsorbent and light stabilizer to the composition is preferred, as moreeffectively improving the weather resistance of the coating films.

The UV absorbent includes, for example, benzophenones, triazoles,phenylsalicylates, diphenylacrylates, acetophenones, etc. One or more ofthese may be used either singly or as combined.

The light stabilizer includes, for example,bis(2,2,6-tetramethyl-4-piperidyl) sebacate,bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate,bis(1,2,2,6,6-pentamethyl-4-piperidyl)2-(3,5-tert-butyl-4-hydroxybenzyl)-2-n-butylmalonate,tetrakis(2,2,6,6-tetramethyl-4-piperidyl) 1,2,3,4-butane-tetracarboxylate, tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)1,2,3,4-butane-tetracarboxylate, etc. One or more of these may be usedeither singly or as combined.

The amount of the UV absorbent is generally from 0.1 to 10 parts byweight, preferably from 1 to 5 parts by weight, relative to 100 parts byweight of the solid resin content of the curable composition; and thatof the light stabilizer is generally from 0.1 to 10 parts by weight,preferably from 1 to 5 parts by weight, relative to 100 parts by weightof the solid resin content of the curable composition.

One embodiment of using the curable composition of the invention forcoating will be mentioned below.

A substrate is first coated with a base coat paint containing metallicpowder and/or color pigment, and then overcoated with a clear paint fortop coat consisting essentially of a curable composition of theinvention.

The base coat paint containing metallic powder and/or color pigment isnot specifically defined. For example, it consists essentially of anaminoalkyd resin, an oil-free alkyd resin, a thermosetting acrylicresin, a thermosetting urethane resin, a nitrocellulose lacquer, amodified acrylic lacquer, a straight acrylic lacquer, a cold-settingurethane resin, an acrylic enamel resin, an oxidation-setting alkydresin, an oxidation-setting, modified alkyd resin (e.g., CAB, etc.), acold-setting or thermosetting fluorine resin, a hydrolyzable silylgroup-having resin, a curable composition of the invention, or a mixtureof those, and containing metallic powder and/or color pigment.

The base coat paint containing metallic powder and/or color pigment maybe of any type, including, for example, a solution-type paint dissolvedin an organic solvent, a non-aqueous dispersion-type paint, amulti-liquid-type paint, a powdery paint, a slurry paint, an aqueouspaint, etc.

The metallic powder and the color pigment are not also specificallydefined, and any conventional ones are employable. Specific examples ofthe metallic powder include, for example, aluminum powder, copperpowder, mica powder, etc.; and those of the color pigment include, forexample, organic pigments such as phthalocyanine blue, toluidine red,benzidine yellow, etc., and inorganic pigments such as titanium oxide,carbon black, red iron oxide, etc. One or more of those metallic powdersand color pigments may be used either singly or as combined.

Adding UV absorbent and light stabilizer such as those mentionedhereinabove to the base coat is recommended, as further improving theweather resistance of the coated articles.

If desired, silicone compounds (aminosilane compounds, etc.) such asthose mentioned above may be added to the base coat paint containingmetallic powder and/or color pigment, by which the adhesiveness betweenthe base coat and the overlying clear top coat may be improved.

In that case, the amount of the silicone compound to be added isgenerally not larger than 20 parts by weight, preferably from 0.5 partsby weight to 10 parts by weight, relative to 100 parts by weight of thebase coat paint containing metallic powder and/or color pigment.

The coated articles of the invention have a clear top coat as paintedover a base coat. For example, they may be produced in a 2-coat 1-bakemethod comprising coating a substrate with a base coat paint containingmetallic powder and/or color pigment such as that mentioned above,setting it as such for a few minutes, then further coating it with aclear top coat paint in an wet-on-wet manner, and finally curing itunder heat; or in a 2-coat 2-bake method comprising coating a substratewith a base coat paint containing metallic powder and/or color pigment,curing it under heat, then coating it with a clear top coat paint, andfurther curing it under heat. The coating with the clear top coat paintmay be attained in any conventional manner of dipping, spraying,brushing, roll-coating or flow-coating. After having been thus coated,the coated paint layer may be cured under heat at a temperature of 30°C. or higher, preferably at a temperature falling between 55 and 350° C.

The thickness of the coating films varies, depending on the use of thecoated articles, and therefore could not be indiscriminately defined.Preferably, however, the thickness of the base coat containing metallicpowder and/or color pigment may fall between 10 and 30 μm in view of itsmasking property; while that of the clear top coat may fall between 20and 50 μm in view of its durability.

The curable composition for top coating of the present invention hadgood thermal curability, and forms good coating films having good acidresistance, good scratch resistance and good outward appearance, andhaving good stain resistance. Therefore, the composition is favorable totop coating, for example, for cars, industrial machines, steelfurniture, interior and exterior decorations for constructions,household electric appliances, plastic goods, etc. The composition isespecially favorable for top coating for cars.

The curable composition for top coating of the invention and alsoarticles coated with it will be described in more detail with referenceto the following Examples, which, however, are not intended to restrictthe scope of the invention.

PRODUCTION EXAMPLES (A-1 to A-6) for Component (A) Production Example 1(E-1) for Component (E)

The components of “Part 2” in Table 1 below were fed into a reactorequipped with a stirrer, a thermometer, a reflux condenser, a nitrogengas duct and a dropping funnel, and heated up to 115° C. whileintroducing nitrogen gas thereinto, and then a mixed solution of “Part1” was dropwise added thereto at a constant rate over a period of 4hours.

Next, a mixed solution of “Part 3” was dropwise added to this at aconstant rate over a period of 1 hour. Then, this was immediatelystirred at 115° C. for 2 hours, and thereafter cooled to roomtemperature. Finally, a mixed solution of “Part 4” was added to this,and stirred.

The solid concentration of the resulting solution, the number-averagemolecular weight of the copolymer as measured through gel permeationchromatography (hereinafter referred to as GPC), the siliconeequivalent, the alcoholic hydroxyl equivalent and the epoxy equivalentare shown in Table 1.

TABLE 1 Production Example for Production Example for Component (A)Component Resin [1] Resin [2] Resin [3] Resin [4] (E) Part CompositionA-1 A-2 A-3 A-4 A-5 A-6 E-1 1 A-174 — — — 35 10 15 — Styrene 20 20 15 1010 10 25 Cyclohexyl Methacrylate 20 20 15 20 15 15 15 2-EthylhexylMethacrylate 35 20 20 25 27 17 36 Glycidyl Methacrylate 25 40 42 10 3830 — 2-Hydroxyethyl Methacrylate — — 8 — — 13 26 Solvesso 100 12 12 128.2 8.2 8.2 12.4 1-Butanol 6 6 6 5.5 5.5 5.5 — V-59 4.75 5.7 5.7 4.755.7 5.7 5.7 2 Solvesso 100 15.5 15.5 15.5 15.6 15.6 15.6 15.5 1-Butanol10.5 10.5 10.5 10.4 10.4 10.4 10.5 3 Xylene 10 10 10 5 5 5 10 V-59 0.250.3 0.3 0.25 0.3 0.3 0.3 4 Methyl Orthoacetate — — — 4 4 4 — Methanol —— — 2 2 2 — Solid Concentration (%) 63 62 64 63 64 63 67 Number-AverageMolecular Weight 5100 4500 4700 5200 4700 4600 4600 Hydrolyzable SilylEquivalent — — — 709 2480 1653 — Alcoholic Hydroxyl Equivalent — — 1625— — 1000 500 Epoxy Equivalent 568 355 338 1420 374 473 — AlcoholicHydroxyl Group/ — — — — — 1.65 — Hydrolyzable Silyl Group A-174:γ-trimethoxysilylpropyl methacrylate (manufactured by Nippon Unicar Co.)V-59: 2,2′-azobis(2-methylbutyronitrile) (manufactured by Wako PureChemical Co.)

Production Examples 1 and 2 for Component (B) (carboxylic acid oligomersB-1 and B-2)

The components of “Part 1” in Table 2 below were fed into a reactorequipped with a stirrer, a thermometer, a reflux condenser, a nitrogengas duct and a dropping funnel, and stirred at 120° C. for 15 minuteswhile introducing nitrogen gas thereinto, and thereafter the componentsof “Part 2” were added thereto over a period of 15 minutes.

Then, these were reacted at 120° C. for 3 hours. The IR absorptionspectrum (hereinunder referred to as IR) of the reaction product wasmeasured, in which the absence of the absorption by acid anhydridegroups (at 1,785 cm⁻¹) was confirmed.

TABLE 2 Production Example for Component (B) Part Composition B-1 B-2 1Triethylamine 0.07 0.07 Pentaerythritol 35 — Trimethylolpropane — 34Propylene Glycol Monomethyl Ether 110 76 Acetate 2Methylhexahydrophthalic Anhydride 169 — Hexahydrophthalic Anhydride —113 Solid Concentration (%) 65 66 Molecular Weight 809 597

Production Example 3 for Component (B) (B-3)

The components of “Part 2” in Table 3 below were fed into a reactorequipped with a stirrer, a thermometer, a reflux condenser, a nitrogengas duct and a dropping funnel, and heated up to 115° C. whileintroducing nitrogen gas thereinto, and then a mixed solution of “Part1” was dropwise added thereto at a constant rate over a period of 4hours.

Next, a mixed solution of “Part 3” was dropwise added to this at aconstant rate over a period of 1 hour. Then, these were immediatelystirred at 115° C. for 2 hours, and then cooled to room temperature.

The solid concentration of the resulting solution, and thenumber-average molecular weight of the copolymer (as measured throughGPC) are Table 3.

TABLE 3 Production Example for Component (B) Part Composition B-3 1Acrylic Acid 20 Styrene 20 2-Ethylhexyl Methacrylate 30 IsobutylMethacrylate 30 Solvesso 100 10 1-Butanol 6 V-59 5.7 2 Solvesso 100 151-Butanol 10 3 Xylene 10 V-59 0.3 Solid Concentration (%) 63Number-Average Molecular Weight 4700

Production Example 4 for Component (B) (B-4)

In the same manner as in Production Example (B-3) except that thecomponents indicated in Table 4 below were used, produced was a polymer(B′-4).

The solid concentration of the resulting solution, and thenumber-average molecular weight of the polymer (B′-4) (as measuredthrough GPC) are shown in Table 4.

TABLE 4 Production Example for Component (B) Part Composition B′-4 1Styrene 15 Cyclohexyl Methacrylate 20 2-Ethylhexyl Acrylate 30 IsobutylMethacrylate 14.5 Maleic Anhydride 20.5 Solvesso 100 20.5 PropyleneGlycol Monomethyl Ether Acetate 4.1 T-butyl Peroxy-2-ethylhexanoate 5.72 Solvesso 100 26 3 Xylene 10 T-butyl Peroxy-2-ethylhexanoate 0.3 SolidConcentration (%) 52 Number-Average Molecular Weight 6000

To 192.3 parts of the resulting polymer (B′-4), added were 1.0 part oftriethylamine as dissolved in 17.6 parts of butyl acetate and 10 partsof methanol, and reacted at 60° C. for 8 hours. Thus was obtained apolymer (B-4). In its IR, confirmed was the complete absence of theabsorption by acid anhydride groups (at 1,785 cm⁻¹).

Production Example 2 for Component (E) (E-2)

The components of “Part 1” in Table 5 below were fed into a reactor, andheated at the refluxing temperature (97° C.). Next, the component of“Part 2” was added thereto, and immediately the components of “Part 3”and “Part 4” were added thereto at a constant rate over a period of 225minutes.

The mixture was transparent in the initial stage, but immediately afterthe addition of the “Part 3” and the “Part 4” thereto, it became paleblue, and then became milky in 40 minutes.

After this, the components of “Part 5” were added to the mixture at aconstant rate over a period of 30 minutes, and then kept at therefluxing temperature for further 90 minutes.

Finally, the excess solvent was removed. Thus was obtained a stabledispersion with no phase separation, which had a solid content of 63.4%and was milky.

The resulting polymer had a Stormer viscosity of 76 KU and a meanparticle size of 300 nm.

The “solution containing organic solvent-soluble polymer” in “Part 1” ofthe starting material was prepared by polymerizing the monomers shown inparenthesis in the solvent also shown in parenthesis. This polymer formsthe arm site (2).

On the other hand, the polymer of methacrylic acid, 2-hydroxyethylacrylate, methyl methacrylate, methyl acrylate, and glycidylmethacrylate in “Part 3” of the starting material forms the core site(1).

TABLE 5 Production Example 2 for Component (E) E-2 Part CompositionAmount 1 Solution Containing Organic Solvent-Soluble Polymer 579 g (Mw =3500) (solution of 62% acrylic polymer composed of 15% of styrene, 28%of butyl methacrylate, 30% of butyl acrylate, 10% of 2-hydroxyethylacrylate, 2% of acrylic acid, and 15% of ethyl methacrylate, in whichthe solvent is a mixture of 82% of xylene and 18% of 1-butanol)Isopropanol 22 g Mineral Sprit 41 g Heptane 460 g Xylene 95 g 2 T-butylPeroctanoate 1 g 3 Methacrylic Acid 40 g 2-Hydroxyethyl Acrylate 250 gMethyl Methacrylate 365 g Methyl Acrylate 180 g Styrene 150 g GlycidylMethacrylate 15 g Solution Containing Organic Solvent-Soluble Polymer290 g (same as in Part 1) Heptane 26 g 4 Mineral Spirit 148 g 1-Butanol26 g T-butyl Peroctanoate 11 g 5 T-butyl Peroctanoate 8 g 1-Butanol 59 gHeptane 6 g

Examples 1 to 8, Comparative Examples 1 to 4

The component (A) [(A-1) to (A-6)], the component (B) [(B-1) to (B-4)]and the component (C) prepared in Production Examples mentioned abovewere formulated in different solid ratios as in Table 6 below.

To the resulting mixtures of Examples and Comparative Examples, addedwere 0.4%, relative to the total solid resin content of each mixture, ofa leveling agent (Kusumoto Chemical's L-1984-50), 2% of an UV absorbent,Tinuvin 384, and 1% of a light stabilizer, Tinuvin 123 (both products ofCiba Geigy).

Next, each mixture was diluted with Solvesso 100 (petroleum-typearomatic solvent, a product of Exxon Chemical) to have a viscositytaking about 20 to about 25 seconds in a Ford cup. Thus were preparedvarious clear paint samples for top coating.

A soft steel sheet was degreased and phosphorylated, and then coatedwith an epoxyamide-based, cationic electrodeposition primer and anintermediate-coating surfacer in that order, the both being for carbodies. The thus-coated sheet was used as a test substrate herein. Thesubstrate was further coated with a commercially-available acrylicmelamine resin-based coating material (black base coat).

Next, the clear paint sample for top coating was applied on thethus-coated-substrate in a wet-on-wet coating manner, set as such for 20minutes, and then baked at 140° C. for 30 minutes.

The dry thickness of the base coat was about 15 μm, and that of theclear top coat was about 50 μm.

The coating films thus formed herein were tested for [1] acidresistance, [2] scratch resistance, [3] storage stability of clear topcoat paints, [4] recoating adhesiveness, [5] accelerated weatherresistance, and [6] pencil hardness, according to the methods mentionedbelow. The test data obtained are shown in Table 6.

[1] Acid Resistance:

0.5 cc of an aqueous solution of 10% sulfuric acid was dripped onto eachcoated sample through a pipette, and then heated in a drier at 80° C.for 30 minutes. After thus dried, the sample was washed with water toremove the sulfuric acid solution, and the condition of the surface ofthe coating film on the sample was visually observed. Each sample wasevaluated according to the following criteria:

Point 10: No change found.

Point 9: Slight change found.

Point 8: Circular marks found.

Point 7: Slightly discolored and swollen.

Point 5: Definitely discolored with definite decrease in surface gloss.

Point 1: Coating film dissolved.

[2] Scratch Resistance (surface gloss retentiveness):

Each coated sample (150×100 mm) was fixed horizontally, to which wasapplied an abrasive (mixture of 1.2% of JIS Type 8 loam, 1.2% of JISType 11 loam, 0.6% of kaolin, 1% of neutral detergent and 96% of water)in an amount of about 0.05 g/cm². In that condition, the surface of thesample was rubbed with a weight covered with kraft paper. The contactsurface of the weight had a diameter of 5 cm, and the load thereof was22 g/cm².

Before and after rubbed for 20 strokes, the surface gloss of the coatingfilm of each sample was measured at an angle of 20°, using a gloss meter(manufactured by Murakami Color Technology Laboratory). The surfacegloss retentiveness (%) of each sample after 20 strokes was obtainedaccording to the following equation.

Surface Gloss Retentiveness (%)=(surface gloss before rubbed/surfacegloss after rubbed)×100

Samples having a higher degree of surface gloss retentiveness havebetter scratch resistance.

[3] Storage Stability:

Clear top coat paint samples as prepared to have a viscosity of 150 cpsat 23° C. were stored at 50° C. for 10 days, and their viscosity (cps at23° C.) was measured with a B-type viscometer. Based on the dataobtained, the storage stability of each sample was evaluated.

[4] Recoating Adhesiveness:

Each coated sample was again coated with the same base coat and thenwith the same clear paint in a wet-on-wet coating manner, in the samemanner as previously. After having been set as such for 20 minutes, thesamples were baked at 120° C. for 30 minutes. The adhesiveness of thecoating film on each sample was measured according to the cross-cutpeeling test (2 mm×2 mm×25) in JIS K 5400.

[5] Accelerated Weather Resistance:

Each sample was evaluated for the accelerated weather resistanceaccording to JIS K 5400, using a sunshine carbon arc lamp weatherresistance tester (manufactured by Suga Shikenki KK).

The test condition was as follows: Each sample was exposed to the carbonarc lamp for 1,500 hours at a black panel temperature of 63±3° C. inrepeated intermittent raining cycles. In one cycle of 120 minutes,raining continued for 18 minutes. After the test, each sample wasvisually observed, and evaluated according to the following criteria:

◯: No change.

◯Δ: Water marks found, or whitened.

Δ: Great water marks found with definite decrease in surface gloss.

[6] Pencil Hardness:

The pencil hardness of each sample was measured according to JIS K 5400.

TABLE 6 Example Comparative Example 1 2 3 4 5 6 7 8 1 2 3 4 (A) A-1 — —— — 70 — — — — — — — A-2 — — — — — — — 50 50 — — — A-3 — — — — — 55 — —— 70 — — A-4 90 65 — — — — — — — — 70 — A-5 — — 70 — — — 70 — — — — —A-6 — — — 70 — — — — — — — 70 (B) B-1 10 — 30 30 20 — — — — — — 30 B-2 —10 — — — 25 — — — 30 — — B-3 — — — — — — 20 — — — 20 — B-4 — — — — — — —50 50 — — — (C) Propylene Glycol — — — 5 — 5 — 5 — — — — MonomethylEther Methyl Cellosolve 5 10 — — — — 5 — — — — — 3,4-Dihydro-2H-pyran —— 5 — — — — — — — — — Tetrahydrofuran — — — — 10 — — — — — — — Methanol5 — 5 5 — — 5 — — — — — Isopropanol — — — — — 5 — 10 — — — — TrimethylOrthoacetate — 5 5 5 5 — — — — — — — (D) Tetraammonium — — — 0.2 — — 0.20.2 0.2 — 0.2 — Bromide Nacure 5225 1.0 1.0 — 1.0 — — 1.0 — — — 1.0 —(E) E-1 — 20 — — — — — — — — — — E-2 — — — — 10 20 10 — — — 10 — (F)Cymel 235 — 5 — — — 5 — — — — — — {circle around (1)} Acid Resistance 1010 10 10 9 9 10 9 9 10 10 10 {circle around (2)} Scratch Resistance(sur- 89 89 84 86 69 72 88 64 62 76 85 86 face gloss retentiveness (%)){circle around (3)} Storage Stability (cps) 182 163 271 312 290 340 224280 >10000 >10000 >10000 >10000 {circle around (4)} RecoatingAdhesiveness 10 10 10 10 10 10 6 5 5 10 5 10 {circle around (5)}Accelerated Weather ∘ ∘ ∘ ∘ ∘ ∘ ∘ Δ ∘ Δ ∘ ∘ ∘ ∘ Resistance {circlearound (6)} Pencil Hardness H F H H HB HB HB HB HB F HB H Molar Ratio(epoxy group/ 1.29 0.92 1.27 1.00 1.25 1.31 1.18 1.35 — — — — carboxylgroup) Nacure 5225: Solution of 25 wt. % blocked sulfonic acid(dodecylbenzenesulfonic acid blocked with dimethyloxazolidine),manufactured by King Industries. Cymel 235: Amino resin, manufactured byMitsui Cytec Co.

From the data in Table 6, it is known that the coating films of thepaints obtained in Examples 1 to 8 all had extremely excellent acidresistance, scratch resistance and weather resistance, and that thepaint compositions of these Examples all had good storage stability.

INDUSTRIAL APPLICABILITY

The curable composition for top coating of the present invention hasgood storage stability and thermal curability, and the coating filmsfrom the composition have well-balanced physical properties in thattheir acid resistance, scratch resistance and appearance, as well astheir weather resistance and stain resistance are all good. Therefore,the composition is favorable to top coating, for example, for cars,industrial machines, steel furniture, interior and exterior decorationsfor constructions, household electric appliances, plastics, etc.

What is claimed is:
 1. A curable composition for coating, which comprises; (A) 100 parts by weight of a resin having at least 2 epoxy groups in one molecule and having an epoxy equivalent of from 200 to 2,000 g/mol, the resin of the component (A) having alcoholic hydroxyl groups in a ratio of not smaller than 400 g/mol in terms of the hydroxyl equivalent, and having hydrolyzable silyl groups in a ratio of not smaller than 500 g/mol in terms of the hydrolyzable silyl equivalent, and (B) from 0.001 to 100 parts by weight of a compound having at least 2 carboxyl groups in one molecule and a molecular weight of not greater than 2.000, in a molar ratio of the epoxy group to the carboxyl group of from 0.2/1 to 5.0/1, and contains; (C) at least one organic solvent selected from glycol monoalkyl ethers, vinyl ethers and cyclic ethers, and at least one selected from monoalkyl alcohol compounds and compounds capable of giving alcohols through hydrolysis, each in an amount of from 1.0 to 30 parts by weight relative to 100 parts by weight of the total solid resin content of the composition.
 2. The curable composition for coating as claimed in claim 1, wherein; the compound of the component (B) is an oligomer compound as obtained through half-esterification of a polyol compound with an acid anhydride.
 3. The curable composition for coating as claimed in claim 1 or 2, which contains; (D) a curing catalyst in an amount of from 0.001 to 10 parts by weight relative to 100 parts by weight of the total solid content of the components (A) and (B).
 4. The curable composition for coating as claimed in claim 1 or 2, which contains; (E) a hydroxyl group-containing resin in an amount of from 0 to 80 parts by weight relative to 100 parts by weight of the total solid content of the components (A) and (B).
 5. The curable composition for coating as claimed in claim 4, wherein the hydroxyl group-having resin of the component (E) is composed of from 5 to 30 parts by weight of at least one, hydroxyl group-having vinylic monomer and from 70 to 95 parts by weight of at least one vinylic monomer having no hydroxyl group, and this is a non-aqueous dispersed polymer to be prepared through dispersion polymerization of at least one, hydroxyl group-having vinylic monomer and at least one vinylic monomer having no hydroxyl group in an organic solution that contains an organic solvent-soluble polymer having a number-average molecular weight of from 1,000 to 25,000, and the non-aqueous dispersed polymer thus prepared is insoluble in said organic solution.
 6. The curable composition for coating as claimed in claim 1 or 2, which contains; (F) an amino resin in an amount of not larger than 30 parts by weight relative to 100 parts by weight of the total solid content of the components (A) and (B).
 7. A coated article having a clear top coat as formed over the surface of the substrate previously coated with a coating composition that contains metallic powder and/or color pigment, wherein; the clear top coat consists essentially of the curable composition for top coating of claim 1 or
 2. 8. The curable composition for coating as claimed in claim 1 or 2, wherein the component (C) contains at least one organic solvent selected from glycol monoalkyl ethers, vinyl ethers and cyclic ethers, a monoalkyl alcohol compound and a compound capable of giving an alcohol through hydrolysis. 